The fabrication of metal tubing of rigid alloys such as steel having a generally elliptical shape poses certain problems. Although tubing of various shapes, including elliptical, can be formed by heating round tubing to a high temperature and working it into the desired shape while heated, this method is excessively costly and time consuming. It is also possible to form round tubing stock into the desired shape by pressing it in a conventional press having two dies as illustrated in FIG. 2; however, to do so requires many successive stages because of a problem discussed below. Accordingly, this method is difficult and time consuming and therefore very expensive.
It is desirable to be able to fabricate tubing having the generally elliptical shape illustrated in FIGS. 1A and 1B by pressing round tubing stock into the desired shape. It will be noted that FIG. 1A represents the cross-sectional shape of tubing which is generally elliptical with substantially flattened sides 103A and 103B which have a radius of curvature which is much greater than that of the round tubing stock from which it could be fabricated as well as the radius of curvature of its substantially rounded sides 104A and 104B, and FIG. 1B represents the cross-sectional shape of generally elliptical tubing in which the flattened sides 101A and 101B are essentially completely flattened with no curvature at all. While it would appear to one of ordinary skill in the art that tubing of the shape illustrated in FIGS. 1A, for example, could be fabricated by pressing round tubing stock between dies having the shape illustrated by those shown at 201 and 202 in FIG. 2, experimental efforts to do this have proved unsuccessful unless performed in an excessive number of stages. When round tubing stock is pressed between two dies having the same general shape as those illustrated at 201 and 202 in FIG. 2, instead of taking the shape defined by the dies, the tubing is initially pressed into the egg shape shown in FIG. 1C and then into the football shape shown in FIG. 1D until the distance w' between the points 120 and 122 on the tubing exceeds the distance shown by the arrows w shown in FIG. 2. This can occur before the surfaces 204 and 206 of the dies 201 and 202, respectively, (in FIG. 2) meet, thereby causing the tubing to crinkle at the points 120 and 122 (in FIG. 1D) before it can be pressed into the shape defined by the dies. This problem is particularly exacerbated when the desired elliptical shape is substantially elongated. The present invention is directed to an apparatus and method for fabricating tubing having the same general shape as that shown in FIGS. 1A or 1B which solves the aforementioned problem of crinkling of the tubing proximate the substantially rounded sides of the tubing when round tubing stock is being pressed into the desired shape.
As used herein, the term "substantially flattened sides" refers to the sides of the tubing fabricated using the present invention which are substantially flattened as shown generally at 101A and 101B in FIG. 1B, or have a radius of curvature which is much larger than that of the round tubing from which it is fabricated, as shown at 103A and 103B in FIG. 1A. The term "substantially rounded sides" refers to the sides of the tubing fabricated using the present invention which are substantially rounded as shown generally at 104A/B and 102A/B in FIGS. 1A and 1B, respectively.
Therefore, it is a primary object of the present invention to provide an apparatus and method for fabricating metal tubing of generally elliptical shape by cold pressing round tubing stock into the desired shape using a press.
It is a further object of the present invention to provide an apparatus for fabricating metal tubing of generally elliptical shape which can be used in conjunction with a press of conventional design having a stationary platen and a moving platen.
It is another object of the present invention to provide an apparatus and method for fabricating metal tubing of generally elliptical shape by pressing round tubing stock into the desired shape which is relatively simple and inexpensive to construct and use.